The present invention is concerned with a test carrier for the analytical investigation of a sample liquid by means of a specific binding reaction of two specific binding partners, one of which is contained in the sample and the other in the reagent system of the test carrier. The test carrier has several capillary-active test zones arranged substantially next to one another on a test layer, which are in liquid contact with one another so that they form a liquid transport path along which a liquid flows by capillary forces from a starting zone to an end zone, a reaction thereby taking place between the first binding partner and the reagent system containing the second binding partner which results in a labelled species characteristic for the desired analysis, the labelled specific species being detected in a detection zone.
For the qualitative and quantitative analytical determinations in the scope of the diagnosis of diseases, so-called carrier-bound tests have recently been increasingly used. In the case of these tests, reagents are embedded in appropriate layers of a solid test carrier which are brought into contact with the sample. The sample is usually a body fluid, such as blood or urine. However, it can also be a liquid obtained by a preceding test step.
Test carriers are known in various forms. The present invention is concerned with those test carriers in which capillary-active test zones, which usually consist of absorbent material layers, for example, papers, fleece or porous synthetic resin layers, are arranged next to one another on a base layer in such a manner that the liquid flows along the liquid path parallel to the base layer. Therefore, these test carriers can also be referred to as "test carriers with longitudinal transport".
Such test carrier constructions are especially advantageous for analysis processes which are based on a specific binding reaction of two bioaffine binding partners. Examples therefor are described in Federal Republic of Germany patent specification No. 34 45 816, to which U.S. Pat. No. 4,861,711 corresponds and in U.S. Pat. No. 4,361,537. Specific binding reactions in this sense are, in particular, immunological interactions, thus reactions between antigens or haptens, on the one hand, and antibodies on the other hand. However, other specific interactions can also be used, such as lectin-sugar or an active material-receptor interaction. In the following, without limitation of the generality, reference is made by way of example to immunological reactions.
Greatly varying test principles can be used which are described in the literature, for example in the two above-mentioned patent specifications.
In a first group of immunological tests, one of the front zones of the liquid transport path contains the first binding partner (analyte) in soluble, labelled form. A test zone provided in the further course of the liquid transport path contains the second binding partner in carrier-fixed form. The analyte from the sample and the labelled analyte from the test compete for the binding positions on the second binding partner. Therefore, such tests are referred to as competitive tests.
In the case of a second group of known immunological tests, one of the front zones of the liquid transport path contains the second binding partner in soluble and labelled form. Due to the specific binding reaction with the first binding partner, mobile and labelled complexes are formed.
In the further course of the test, a further binding partner can be present in carrier-fixed form which is specifically bindable with a binding site of the first or second binding partner not saturated by the complex formation, a sandwich thereby resulting of at least three binding partners. Therefore, such tests are also referred to as sandwich tests.
In the case of the so-called immunoenzymometric (IEMA) principle, the further course of the test contains the analytes in carrier-fixed form, the noncomplexed part of the second binding partner thereby being fixed. Only the complexes remain mobile and can be detected.
It is common to all immunological determinations that the analysis reaction, which inter alia includes a specific binding reaction between the two binding partners, leads to a labelled species characteristic for the desired analysis. In the case of the competitive test, this is the analyte which is bound or which remains free. In the case of the sandwich test, these are the bound sandwich complexes. In the case of the IEMA test, it is the complex which remains freely mobile.
More detailed explanations of the various known immunological test principles are not necessary because they can be found in the appropriate literature. Independently of the special course of the test, the present invention can be advantageously used but it is, nevertheless, specially directed towards test carriers which work according to IEMA principle.
Various immunological processes of determination also differ with regard to the label employed. The present invention is especially concerned with enzyme immune tests in which an enzyme label is used. The labelling enzyme is usually detected by the colour-forming reaction of a substrate of the labelling enzyme. The substrate can, depending upon the carrying out of the test, already be present in the detection zone or can be added thereto. In principle, the present invention can also be used for non-enzymatic processes in which, for example, a coloured material or a radioactive element is used for the labelling.